Improved uplink spectrum efficiency

ABSTRACT

Methods and systems are disclosed for reducing control signaling in uplink transmissions. A device, such as a wireless transmit/receive unit, may determine to use a demodulation reference signal (DM-RS) transmission schedule out of a plurality of DM-RS transmission schedules. The DM-RS transmission schedule may be characterized by a DM-RS transmission being mapped to a single orthogonal frequency-division multiplexing (OFDM) symbol per subframe of a data stream. The DM-RS transmission schedule may be characterized by a DM-RS transmission being mapped to a first subset of subcarriers of an OFDM symbol of a subframe of a data stream and Physical Uplink Shared Channel (PUSCH) transmission or Physical Uplink Control Channel (PUCCH) control information being mapped to a second set of subcarriers of the OFDM symbol. The first set of subcarriers may be different than the second set of subcarriers. The data stream may be transmitted according to the DM-RS transmission schedule.

BACKGROUND

A demodulation reference symbol (DM-RS) may be provided for channelestimation for coherent demodulation. DM-RSs may be associated withphysical uplink shared channel (PUSCH) data and/or physical uplinkcontrol channel (PUSCCH) control transmission. DM-RSs may be present inevery transmitted uplink time slot.

FIG. 2A is a diagram of a prior art mapping of DM-RS transmission in asubframe with a normal cyclic prefix. FIG. 2B is a diagram of a priorart mapping of DM-RS transmission in a subframe with an extended cyclicprefix. FIG. 2C is a diagram of a prior art mapping of DM-RStransmission amongst subcarriers in a subframe with a normal cyclicprefix. A DM-RS may be mapped to an orthogonal frequency-divisionmultiplexing (OFDM) symbol of each time slot. As shown in FIG. 2A, fornormal cyclic prefix, the DM-RS may be mapped to the fourth OFDM symbolof each time slot. As shown in FIG. 2B, for extended cyclic prefix, theDM-RS may be mapped to the third OFDM symbol of each time slot. As shownin FIG. 2C, the DM-RS may be mapped to every subcarrier of an OFDMsymbol for which it is mapped.

SUMMARY

Methods and systems are disclosed for reducing control signaling, forexample, in uplink transmissions. For example, in order to limit thecontrol signaling transmitted by a wireless transit/receive unit (WTRU),a DM-RS transmission schedule may be defined such that fewer DM-RSs aretransmitted as compared to previous LTE releases. In an example, thelocation and/or coding of the DM-RS transmissions may be different thanthat of previous LTE releases in order to reduce signaling overhead.Methods and systems are disclosed for dynamically switching betweenuplink DM-RS transmission schedule and for performing retransmissionwith dynamic uplink DM-RS transmission schedule switching.

A WTRU may include a processor. The processor may be configured todetermine to use a demodulation reference signal (DM-RS) transmissionschedule. For example, the processor may determine to use a DM-RStransmission schedule out of a plurality of DM-RS transmissionschedules. The DM-RS transmission schedule may be characterized by aDM-RS transmission being mapped to a single orthogonalfrequency-division multiplexing (OFDM) symbol of a subframe of a datastream. As such, the DM-RS transmission may be mapped to a single timeslot of the subframe. A DM-RS transmission may refer to one or moreDM-RSs.

The OFDM symbol may be associated with a first time slot of the subframeand the DM-RS transmission schedule may be characterized by PhysicalUplink Shared Channel (PUSCH) transmission and/or Physical UplinkControl Channel (PUCCH) control information being mapped to acorresponding OFDM symbol of a second time slot of the subframe of thedata stream. The OFDM symbol may be associated with a second time slotof the subframe and the DM-RS transmission schedule may be characterizedby PUSCH transmission and/or PUCCH control information being mapped to acorresponding OFDM symbol of a first time slot of the subframe of thedata stream. A corresponding OFDM symbol of a time slot may refer to anOFDM symbol of another time slot that has the same relative time orposition (e.g., the nth OFDM symbol of the time slots would becorresponding OFDM symbols).

The OFDM symbol may be a last OFDM symbol (e.g., the OFDM symbol inposition six or seven depending of the cyclic prefix (CP)) of a firsttime slot of the subframe. The OFDM symbol may be a first OFDM symbol(e.g., the OFDM symbol in position one) of a second time slot of thesubframe.

The DM-RS transmission schedule may be characterized by the DM-RStransmission being mapped to an OFDM symbol of a first time slot of afirst subframe of the data stream and DM-RS transmission being mapped toan OFDM symbol of a second time slot of a second subframe of the datastream. The OFDM symbol of the first subframe may be in the sametemporal position or a different temporal position as the OFDM symbol ofthe second subframe. The temporal position of an OFDM symbol may referto the relative time location (e.g., nth OFDM symbol) of the OFDM symbolwithin a time slot.

The DM-RS transmission schedule may be characterized by a DM-RStransmission being mapped to a first subset of subcarriers of an OFDMsymbol of a subframe of a data stream and PUSCH transmission and/orPUCCH control information being mapped to a second set of subcarriers ofthe OFDM symbol. The first set of subcarriers may be different than thesecond set of subcarriers. The first subset of the subcarriers of theOFDM symbol may be half of the subcarriers of the OFDM symbol. The firstsubset of subcarriers of the OFDM symbol may be the first sixsubcarriers of a physical resource block of the OFDM symbol. The firstsubset of subcarrier of the OFDM symbol may be the last six subcarriersof a physical resource block of the OFDM symbol. The first subset of thesubcarriers of the OFDM symbol may be an integer multiple of twelve. Thefirst subset of subcarriers may be even numbered subcarriers and thesecond subset of subcarriers may be odd numbered subcarriers. The firstsubset of subcarriers may be odd numbered subcarriers and the secondsubset of subcarriers may be even numbered subcarriers.

The processor may be configured to transmit the data stream according tothe DM-RS transmission schedule. The data stream may include PUSCHtransmission and/or PUCCH control information. The processor maydetermine to use the DM-RS transmission schedule based on whether theWTRU is connected to a small cell and/or based on whether the WTRU isconnected to a macro cell. The plurality of DM-RS transmission schedulesmay include one or more legacy DM-RS transmission schedules.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a system diagram of an example communications system in whichone or more disclosed embodiments may be implemented.

FIG. 1B is a system diagram of an example wireless transmit/receive unit(WTRU) that may be used within the communications system illustrated inFIG. 1A.

FIG. 1C is a system diagram of an example radio access network and anexample core network that may be used within the communications systemillustrated in FIG. 1A.

FIG. 1D is a system diagram of another example radio access network andan example core network that may be used within the communicationssystem illustrated in FIG. 1A.

FIG. 1E is a system diagram of another example radio access network andan example core network that may be used within the communicationssystem illustrated in FIG. 1A.

FIG. 2A is a diagram of a prior art mapping of demodulation referencesymbols (DM-RS) transmission in a subframe with a normal cyclic prefix.

FIG. 2B is a diagram of a prior art mapping of DM-RS transmission in asubframe with an extended cyclic prefix.

FIG. 2C is a diagram of a prior art mapping of DM-RS transmissionamongst subcarriers in a subframe with a normal cyclic prefix.

FIG. 3A is a diagram of an example mapping of DM-RS transmission in afirst time slot of a subframe with a normal cyclic prefix.

FIG. 3B is a diagram of an example mapping of DM-RS transmission in asecond time slot of a subframe with a normal cyclic prefix.

FIG. 4 is a diagram of an example mapping of DM-RS transmission that maybe shifted towards the edge of a time slot of a subframe with a normalcyclic prefix.

FIG. 5 is a diagram of an example mapping of DM-RS transmission in twosubframes using subframe bundling with a normal cyclic prefix.

FIG. 6 is a diagram of an example mapping of DM-RS transmission in asubset of subcarriers of orthogonal frequency-division multiplexing(OFDM) symbols of two time slots of a subframe.

FIG. 7 is a diagram of an example mapping of DM-RS transmission in asubset of subcarriers of OFDM symbols of two time slots of a subframe.

DETAILED DESCRIPTION

A detailed description of illustrative embodiments will now be describedwith reference to the various Figures. Although this descriptionprovides a detailed example of possible implementations, it should benoted that the details are intended to be exemplary and in no way limitthe scope of the application.

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed embodiments may be implemented. The communicationssystem 100 may be a multiple access system that provides content, suchas voice, data, video, messaging, broadcast, etc., to multiple wirelessusers. The communications system 100 may enable multiple wireless usersto access such content through the sharing of system resources,including wireless bandwidth. For example, the communications systems100 may employ one or more channel access methods, such as code divisionmultiple access (CDMA), time division multiple access (TDMA), frequencydivision multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrierFDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include wirelesstransmit/receive units (WTRUs) 102 a, 102 b, 102 c, and/or 102 d (whichgenerally or collectively may be referred to as WTRU 102), a radioaccess network (RAN) 103/104/105, a core network 106/107/109, a publicswitched telephone network (PSTN) 108, the Internet 110, and othernetworks 112, though it will be appreciated that the disclosedembodiments contemplate any number of WTRUs, base stations, networks,and/or network elements. Each of the WTRUs 102 a, 102 b, 102 c, 102 dmay be any type of device configured to operate and/or communicate in awireless environment. By way of example, the WTRUs 102 a, 102 b, 102 c,102 d may be configured to transmit and/or receive wireless signals andmay include user equipment (UE), a mobile station, a fixed or mobilesubscriber unit, a pager, a cellular telephone, a personal digitalassistant (PDA), a smartphone, a laptop, a netbook, a personal computer,a wireless sensor, consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106/107/109, theInternet 110, and/or the networks 112. By way of example, the basestations 114 a, 114 b may be a base transceiver station (BTS), a Node-B,an eNode B, a Home Node B, a Home eNode B, a site controller, an accesspoint (AP), a wireless router, and the like. While the base stations 114a, 114 b are each depicted as a single element, it will be appreciatedthat the base stations 114 a, 114 b may include any number ofinterconnected base stations and/or network elements.

The base station 114 a may be part of the RAN 103/104/105, which mayalso include other base stations and/or network elements (not shown),such as a base station controller (BSC), a radio network controller(RNC), relay nodes, etc. The base station 114 a and/or the base station114 b may be configured to transmit and/or receive wireless signalswithin a particular geographic region, which may be referred to as acell (not shown). The cell may further be divided into cell sectors. Forexample, the cell associated with the base station 114 a may be dividedinto three sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, e.g., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 115/116/117,which may be any suitable wireless communication link (e.g., radiofrequency (RF), microwave, infrared (IR), ultraviolet (UV), visiblelight, etc.). The air interface 115/116/117 may be established using anysuitable radio access technology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 103/104/105 and the WTRUs 102a, 102 b, 102 c may implement a radio technology such as UniversalMobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA),which may establish the air interface 115/116/117 using wideband CDMA(WCDMA). WCDMA may include communication protocols such as High-SpeedPacket Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA may includeHigh-Speed Downlink Packet Access (HSDPA) and/or High-Speed UplinkPacket Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface115/116/117 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (e.g.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106/107/109.

The RAN 103/104/105 may be in communication with the core network106/107/109, which may be any type of network configured to providevoice, data, applications, and/or voice over internet protocol (VoIP)services to one or more of the WTRUs 102 a, 102 b, 102 c, 102 d. Forexample, the core network 106/107/109 may provide call control, billingservices, mobile location-based services, pre-paid calling, Internetconnectivity, video distribution, etc., and/or perform high-levelsecurity functions, such as user authentication. Although not shown inFIG. 1A, it will be appreciated that the RAN 103/104/105 and/or the corenetwork 106/107/109 may be in direct or indirect communication withother RANs that employ the same RAT as the RAN 103/104/105 or adifferent RAT. For example, in addition to being connected to the RAN103/104/105, which may be utilizing an E-UTRA radio technology, the corenetwork 106/107/109 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106/107/109 may also serve as a gateway for the WTRUs102 a, 102 b, 102 c, 102 d to access the PSTN 108, the Internet 110,and/or other networks 112. The PSTN 108 may include circuit-switchedtelephone networks that provide plain old telephone service (POTS). TheInternet 110 may include a global system of interconnected computernetworks and devices that use common communication protocols, such asthe transmission control protocol (TCP), user datagram protocol (UDP)and the internet protocol (IP) in the TCP/IP internet protocol suite.The networks 112 may include wired or wireless communications networksowned and/or operated by other service providers. For example, thenetworks 112 may include another core network connected to one or moreRANs, which may employ the same RAT as the RAN 103/104/105 or adifferent RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, e.g., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B is a system diagram of an example WTRU 102. As shown in FIG. 1B,the WTRU 102 may include a processor 118, a transceiver 120, atransmit/receive element 122, a speaker/microphone 124, a keypad 126, adisplay/touchpad 128, non-removable memory 130, removable memory 132, apower source 134, a global positioning system (GPS) chipset 136, andother peripherals 138. It will be appreciated that the WTRU 102 mayinclude any sub-combination of the foregoing elements while remainingconsistent with an embodiment. Also, embodiments contemplate that thebase stations 114 a and 114 b, and/or the nodes that base stations 114 aand 114 b may represent, such as but not limited to transceiver station(BTS), a Node-B, a site controller, an access point (AP), a home node-B,an evolved home node-B (eNodeB), a home evolved node-B (HeNB), a homeevolved node-B gateway, and proxy nodes, among others, may include someor all of the elements depicted in FIG. 1B and described herein.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it will be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 115/116/117. For example, in one embodiment,the transmit/receive element 122 may be an antenna configured totransmit and/or receive RF signals. In another embodiment, thetransmit/receive element 122 may be an emitter/detector configured totransmit and/or receive IR, UV, or visible light signals, for example.In yet another embodiment, the transmit/receive element 122 may beconfigured to transmit and receive both RF and light signals. It will beappreciated that the transmit/receive element 122 may be configured totransmit and/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 115/116/117.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 115/116/117from a base station (e.g., base stations 114 a, 114 b) and/or determineits location based on the timing of the signals being received from twoor more nearby base stations. It will be appreciated that the WTRU 102may acquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C is a system diagram of the RAN 103 and the core network 106according to an embodiment. As noted above, the RAN 103 may employ aUTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102 cover the air interface 115. The RAN 103 may also be in communicationwith the core network 106. As shown in FIG. 1C, the RAN 103 may includeNode-Bs 140 a, 140 b, 140 c, which may each include one or moretransceivers for communicating with the WTRUs 102 a, 102 b, 102 c overthe air interface 115. The Node-Bs 140 a, 140 b, 140 c may each beassociated with a particular cell (not shown) within the RAN 103. TheRAN 103 may also include RNCs 142 a, 142 b. It will be appreciated thatthe RAN 103 may include any number of Node-Bs and RNCs while remainingconsistent with an embodiment.

As shown in FIG. 1C, the Node-Bs 140 a, 140 b may be in communicationwith the RNC 142 a. Additionally, the Node-B 140 c may be incommunication with the RNC142 b. The Node-Bs 140 a, 140 b, 140 c maycommunicate with the respective RNCs 142 a, 142 b via an Iub interface.The RNCs 142 a, 142 b may be in communication with one another via anIur interface. Each of the RNCs 142 a, 142 b may be configured tocontrol the respective Node-Bs 140 a, 140 b, 140 c to which it isconnected. In addition, each of the RNCs 142 a, 142 b may be configuredto carry out or support other functionality, such as outer loop powercontrol, load control, admission control, packet scheduling, handovercontrol, macrodiversity, security functions, data encryption, and thelike.

The core network 106 shown in FIG. 1C may include a media gateway (MGW)144, a mobile switching center (MSC) 146, a serving GPRS support node(SGSN) 148, and/or a gateway GPRS support node (GGSN) 150. While each ofthe foregoing elements are depicted as part of the core network 106, itwill be appreciated that any one of these elements may be owned and/oroperated by an entity other than the core network operator.

The RNC 142 a in the RAN 103 may be connected to the MSC 146 in the corenetwork 106 via an IuCS interface. The MSC 146 may be connected to theMGW 144. The MSC 146 and the MGW 144 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices.

The RNC 142 a in the RAN 103 may also be connected to the SGSN 148 inthe core network 106 via an IuPS interface. The SGSN 148 may beconnected to the GGSN 150. The SGSN 148 and the GGSN 150 may provide theWTRUs 102 a, 102 b, 102 c with access to packet-switched networks, suchas the Internet 110, to facilitate communications between and the WTRUs102 a, 102 b, 102 c and IP-enabled devices.

As noted above, the core network 106 may also be connected to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

FIG. 1D is a system diagram of the RAN 104 and the core network 107according to an embodiment. As noted above, the RAN 104 may employ anE-UTRA radio technology to communicate with the WTRUs 102 a, 102 b, 102c over the air interface 116. The RAN 104 may also be in communicationwith the core network 107.

The RAN 104 may include eNode-Bs 160 a, 160 b, 160 c, though it will beappreciated that the RAN 104 may include any number of eNode-Bs whileremaining consistent with an embodiment. The eNode-Bs 160 a, 160 b, 160c may each include one or more transceivers for communicating with theWTRUs 102 a, 102 b, 102 c over the air interface 116. In one embodiment,the eNode-Bs 160 a, 160 b, 160 c may implement MIMO technology. Thus,the eNode-B 160 a, for example, may use multiple antennas to transmitwireless signals to, and receive wireless signals from, the WTRU 102 a.

Each of the eNode-Bs 160 a, 160 b, 160 c may be associated with aparticular cell (not shown) and may be configured to handle radioresource management decisions, handover decisions, scheduling of usersin the uplink and/or downlink, and the like. As shown in FIG. 1D, theeNode-Bs 160 a, 160 b, 160 c may communicate with one another over an X2interface.

The core network 107 shown in FIG. 1D may include a mobility managementgateway (MME) 162, a serving gateway 164, and a packet data network(PDN) gateway 166. While each of the foregoing elements are depicted aspart of the core network 107, it will be appreciated that any one ofthese elements may be owned and/or operated by an entity other than thecore network operator.

The MME 162 may be connected to each of the eNode-Bs 160 a, 160 b, 160 cin the RAN 104 via an S1 interface and may serve as a control node. Forexample, the MME 162 may be responsible for authenticating users of theWTRUs 102 a, 102 b, 102 c, bearer activation/deactivation, selecting aparticular serving gateway during an initial attach of the WTRUs 102 a,102 b, 102 c, and the like. The MME 162 may also provide a control planefunction for switching between the RAN 104 and other RANs (not shown)that employ other radio technologies, such as GSM or WCDMA.

The serving gateway 164 may be connected to each of the eNode-Bs 160 a,160 b, 160 c in the RAN 104 via the S1 interface. The serving gateway164 may generally route and forward user data packets to/from the WTRUs102 a, 102 b, 102 c. The serving gateway 164 may also perform otherfunctions, such as anchoring user planes during inter-eNode B handovers,triggering paging when downlink data is available for the WTRUs 102 a,102 b, 102 c, managing and storing contexts of the WTRUs 102 a, 102 b,102 c, and the like.

The serving gateway 164 may also be connected to the PDN gateway 166,which may provide the WTRUs 102 a, 102 b, 102 c with access topacket-switched networks, such as the Internet 110, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and IP-enableddevices.

The core network 107 may facilitate communications with other networks.For example, the core network 107 may provide the WTRUs 102 a, 102 b,102 c with access to circuit-switched networks, such as the PSTN 108, tofacilitate communications between the WTRUs 102 a, 102 b, 102 c andtraditional land-line communications devices. For example, the corenetwork 107 may include, or may communicate with, an IP gateway (e.g.,an IP multimedia subsystem (IMS) server) that serves as an interfacebetween the core network 107 and the PSTN 108. In addition, the corenetwork 107 may provide the WTRUs 102 a, 102 b, 102 c with access to thenetworks 112, which may include other wired or wireless networks thatare owned and/or operated by other service providers.

FIG. 1E is a system diagram of the RAN 105 and the core network 109according to an embodiment. The RAN 105 may be an access service network(ASN) that employs IEEE 802.16 radio technology to communicate with theWTRUs 102 a, 102 b, 102 c over the air interface 117. As will be furtherdiscussed below, the communication links between the differentfunctional entities of the WTRUs 102 a, 102 b, 102 c, the RAN 105, andthe core network 109 may be defined as reference points.

As shown in FIG. 1E, the RAN 105 may include base stations 180 a, 180 b,180 c, and an ASN gateway 182, though it will be appreciated that theRAN 105 may include any number of base stations and ASN gateways whileremaining consistent with an embodiment. The base stations 180 a, 180 b,180 c may each be associated with a particular cell (not shown) in theRAN 105 and may each include one or more transceivers for communicatingwith the WTRUs 102 a, 102 b, 102 c over the air interface 117. In oneembodiment, the base stations 180 a, 180 b, 180 c may implement MIMOtechnology. Thus, the base station 180 a, for example, may use multipleantennas to transmit wireless signals to, and receive wireless signalsfrom, the WTRU 102 a. The base stations 180 a, 180 b, 180 c may alsoprovide mobility management functions, such as handoff triggering,tunnel establishment, radio resource management, traffic classification,quality of service (QoS) policy enforcement, and the like. The ASNgateway 182 may serve as a traffic aggregation point and may beresponsible for paging, caching of subscriber profiles, routing to thecore network 109, and the like.

The air interface 117 between the WTRUs 102 a, 102 b, 102 c and the RAN105 may be defined as an R1 reference point that implements the IEEE802.16 specification. In addition, each of the WTRUs 102 a, 102 b, 102 cmay establish a logical interface (not shown) with the core network 109.The logical interface between the WTRUs 102 a, 102 b, 102 c and the corenetwork 109 may be defined as an R2 reference point, which may be usedfor authentication, authorization, IP host configuration management,and/or mobility management.

The communication link between each of the base stations 180 a, 180 b,180 c may be defined as an R8 reference point that includes protocolsfor facilitating WTRU handovers and the transfer of data between basestations. The communication link between the base stations 180 a, 180 b,180 c and the ASN gateway 182 may be defined as an R6 reference point.The R6 reference point may include protocols for facilitating mobilitymanagement based on mobility events associated with each of the WTRUs102 a, 102 b, 102 c.

As shown in FIG. 1E, the RAN 105 may be connected to the core network109. The communication link between the RAN 105 and the core network 109may defined as an R3 reference point that includes protocols forfacilitating data transfer and mobility management capabilities, forexample. The core network 109 may include a mobile IP home agent(MIP-HA) 184, an authentication, authorization, accounting (AAA) server186, and a gateway 188. While each of the foregoing elements aredepicted as part of the core network 109, it will be appreciated thatany one of these elements may be owned and/or operated by an entityother than the core network operator.

The MIP-HA may be responsible for IP address management, and may enablethe WTRUs 102 a, 102 b, 102 c to roam between different ASNs and/ordifferent core networks. The MIP-HA 184 may provide the WTRUs 102 a, 102b, 102 c with access to packet-switched networks, such as the Internet110, to facilitate communications between the WTRUs 102 a, 102 b, 102 cand IP-enabled devices. The AAA server 186 may be responsible for userauthentication and for supporting user services. The gateway 188 mayfacilitate interworking with other networks. For example, the gateway188 may provide the WTRUs 102 a, 102 b, 102 c with access tocircuit-switched networks, such as the PSTN 108, to facilitatecommunications between the WTRUs 102 a, 102 b, 102 c and traditionalland-line communications devices. In addition, the gateway 188 mayprovide the WTRUs 102 a, 102 b, 102 c with access to the networks 112,which may include other wired or wireless networks that are owned and/oroperated by other service providers.

Although not shown in FIG. 1E, it will be appreciated that the RAN 105may be connected to other ASNs and the core network 109 may be connectedto other core networks. The communication link between the RAN 105 theother ASNs may be defined as an R4 reference point, which may includeprotocols for coordinating the mobility of the WTRUs 102 a, 102 b, 102 cbetween the RAN 105 and the other ASNs. The communication link betweenthe core network 109 and the other core networks may be defined as an R5reference, which may include protocols for facilitating interworkingbetween home core networks and visited core networks.

In order to increase system capacity and provide service to anincreasing number of devices (e.g., such as a wireless transmit/receiveunit (WTRU)), a deployment that includes a layer of small cells inaddition to macro cells may be considered. For example, a layer of smallcells may be configured to operate either in a separate frequency bandand/or in the same frequency band than the one used by the macro celllayer. The use of such deployments may result in additional capacitybeing provided via the use of additional spectrum, via cell reuse,and/or due to spectrum efficiency gains that may be achieved due to thechannel characteristics of the small cell environment. For example, thedistribution of path loss between the small cell and a connected devicemay be such that large values of signal-to-noise-ratio are achieved morefrequently.

The current Long Term Evolution (LTE) specifications are targeted tosupport a wide range of deployments in terms of cell sizes,environments, and device speeds. As a result, the LTE Release 8 and/orRelease 10 physical layer may have been designed and configured in sucha way as to meet diverse deployment scenarios. Therefore, the LTEphysical layer may not be currently configured in a manner capable oftaking full advantage of specific channel characteristics of a smallcell environment. For example, uplink coverage may be enhanced via avariety of physical layer techniques that may be designed to operatespecifically in the small cell environment.

Examples of small cells may include low-powered radio access nodes(e.g., NBs and/or eNBs) that operate in licensed and unlicensedspectrum, for example, that may have a range of 10 meters to 200 meters(e.g., compared to a mobile macrocell which might have a range of a fewkilometers). To support the growth in mobile data traffic, the networkmay use the small cells to perform data offloading, which may result ina more efficient use of radio spectrum. Such use of small cells for dataoffloading may facilitate the management of LTE Advanced spectrum moreefficiently compared to using just macrocells.

Small cells may include one or more of femtocells, picocells, and/ormicrocells. Small-cell networks may also be realized using distributedradio technology, for example centralized baseband units and remoteradio heads. Beamforming techniques (e.g., focusing a radiosignal/energy on a very specific area) may be utilized to furtherenhance or focus small cell coverage. A common factor in many approachesutilized to deploy small cells may be central management of the smallcells by mobile network operators.

Small cells may be deployed on a wide range of air interfaces, forexample including GSM, CDMA2000, Time Division Synchronous Code DivisionMultiple Access (TD-SCDMA), WCDMA, LTE, WiMax, and/or the like. In thirdgeneration partnership project (3GPP) terminology, a Home Node B (HNB)may be configured to serve a femtocell and/or some other type of smallcell. A Home eNode B (HeNB) may be configured to serve an LTE femtocelland/or or some other type of small cell. A Wi-Fi network may be anexample of a small cell that does not operate in licensed spectrum. As aresult, it may be more difficult to manage Wi-Fi deployments effectivelyas compared to small cells that utilize licensed spectrum under thecontrol of a network operator.

A form of small cells is femtocells. Femtocells were initially designedfor residential and small business use, with a short range and a limitednumber of channels. Femtocells with increased range and capacity spawneda proliferation of terms including metrocells, metro femtocells, publicaccess femtocells, enterprise femtocells, super femtos, Class 3 femto,greater femtos, and microcells. The term “small cells” may be used as anumbrella term to describe deployments that utilize one of more of thesetypes of lower power and/or limited range cells.

In order to achieve the potential system throughput gains that may beprovided via an efficient small cell deployment, the access system maybe designed in such a way as to limit the amount of resources that areconsumed by overhead. For example, a source of potential overhead mayinclude resources used up by physical signals that do not include userdata. An example of physical layer resources that may not carry userinformation are demodulation reference signals (DM-RSs). Therefore, oneor more of the following techniques may be used to modify DM-RStransmission, for example, for small cell deployments to facilitateefficient small cell spectrum use. The methods and systems describedherein may be used in any combination.

Although examples to reduce physical layer overhead in order to improveresource utilization may be described with reference to small cellenvironments, the examples and techniques described herein may beequally applicable to deployment in macro cell environments. Therefore,although certain benefits may be achieved by using the methods andsystems described herein in a small cell deployment, embodimentscontemplate the utilization of these techniques in macro deployments,and thus this disclosure should not be read to limit the techniques tosmall cell deployments alone.

As an example, a WTRU may be able to reduce overhead by altering thetransmission schedule for DM-RSs and/or by reducing the overalltransmission of DM-RSs within the system. For example, the DM-RSoverhead may be reduced by decreasing the number of resource elements(REs) used to transmit DM-RSs. The reduction of DM-RS transmission maybe performed in the time domain and/or in the frequency domain. Forexample, DM-RS transmission may be limited in the time domain bylimiting the number of times a given frequency resource may be used forDM-RS transmission per subframe and/or per transmission time interval(TTI). For example, the WTRU may be configured to use a subcarrier suchthat the subcarrier has a single DM-RS symbol per subframe. In anexample, DM-RS overhead reduction may be achieve in the frequencydomain, for example by utilizing an OFDM symbol for a combination ofPUSCH transmission and DM-RS transmission. Furthermore, hybridcombinations of time and/or frequency DM-RS transmission limitations maybe utilized in order to reduce DM-RS transmission overhead.

A DM-RS transmission may refer to one or more DM-RSs. For example, aDM-RS transmission may be characterized by one or more DM-RSs that maybe distributed across one or more REs, one or more PRBs, one or moretime slots, one or more OFDM symbols, and/or one or more subframes of adata stream. A WTRU may be configured to select between one or moredifferent DM-RS transmission schedules. A DM-RS transmission schedulemay be characterized by one or more of the examples described herein. ADM-RS transmission configuration may refer to one or more DM-RStransmission schedules that may be used in one or more differentsubframes.

In an example, a DM-RS transmission may be characterized by a DM-RSbeing transmitted in a single OFDM symbol within a subframe instead oftwo OFDM symbols per subframe. If a DM-RS is transmitted in a singleOFDM symbol per subframe, then the DM-RS would be transmitted in asingle time slot of the two time slots of a subframe. As such, the DM-RSmay be mapped to a single OFDM symbol of a subframe of a data stream.

If fewer OFDM symbols are used for DM-RS transmission, then one or moreREs that were previously used for DM-RS transmission (e.g., according toRelease 8/10) may instead be used for user data transmission and/orcontrol signaling (e.g., via the PUSCH and/or the PUCCH). For example,in Release 8/10, the fourth symbol in the time slot (e.g., third symbolfor extended cyclic prefix) may be used to transmit a DM-RS (e.g., asshown in FIG. 2A). In an example, the fourth symbol in the time slot(e.g., third symbol for extended cyclic prefix) may be used fortransmission of a DM-RS in one of the time slots of a subframe, but notfor the other time slot of the subframe. Instead, the symbol that waspreviously used for DM-RS transmission may be used for PUSCHtransmission and/or for some other UL channel.

FIG. 3A is a diagram of an example mapping of a DM-RS transmission in afirst time slot of a subframe with a normal cyclic prefix. As shown inFIG. 3A, a subframe 300 may include two time slots, a first time slot302 and a second time slot 304. A DM-RS transmission 306 may be includedin an OFDM symbol, such as the fourth OFDM symbol 308, of the first timeslot 302 of the subframe 300. The DM-RS transmission 306 may be absentfrom the second time slot 304 of the subframe 300. For example, thefourth OFDM symbol of the second time slot 304 may include user dataand/or control signaling as opposed to a DM-RS. Although illustrated asbeing included in the fourth OFDM symbol 308 of the first time slot 302,the DM-RS transmission 306 may be included in any OFDM symbol of thefirst time slot 302.

FIG. 3B is a diagram of an example mapping of DM-RS transmission in asecond time slot of a subframe with a normal cyclic prefix. As shown inFIG. 3B, a subframe 310 may include two time slots, a first time slot312 and a second time slot 314. A DM-RS transmission 316 may be includedin an OFDM symbol, such as the fourth OFDM symbol 318, of the secondtime slot 314 of the subframe 310. The DM-RS transmission 316 may beabsent from the first time slot 312 of the subframe 310. For example,the fourth OFDM symbol of the first time slot 312 may include user dataand/or control signaling. Although illustrated as being included in thefourth OFDM symbol 318 of the second time slot 314, the DM-RStransmission 316 may be included in any OFDM symbol of the second timeslot 314.

A WTRU may be configured to determine to use a DM-RS transmissionschedule, for example, out of a plurality of DM-RS transmissionschedules. The DM-RS transmission schedule may be characterized by aDM-RS transmission being mapped to a single OFDM symbol of a subframe ofa data stream. As such, the DM-RS transmission may be mapped to a singletime slot of the subframe. The OFDM symbol may be associated with afirst time slot of the subframe and the DM-RS transmission schedule maybe characterized by Physical Uplink Shared Channel (PUSCH) transmissionand/or Physical Uplink Control Channel (PUCCH) control information beingmapped to a corresponding OFDM symbol of a second time slot of thesubframe of the data stream (e.g., as shown in FIG. 3A). The OFDM symbolmay be associated with a second time slot of the subframe and the DM-RStransmission schedule may be characterized by PUSCH transmission and/orPUCCH control information being mapped to a corresponding OFDM symbol ofa first time slot of the subframe of the data stream (e.g., as shown inFIG. 3B). A corresponding OFDM symbol of a time slot may refer to anOFDM symbol of another time slot that has the same relative time orposition (e.g., the nth OFDM symbol of the time slots would becorresponding OFDM symbols).

The identity of a time slot that includes a DM-RS transmission may bevaried across a plurality of subframes, for example, if a single slotper subframe includes an OFDM symbol with the DM-RS transmission. Theidentity of a time slot may refer to the number or temporal position ofthe time slot within a subframe (e.g., first time slot or second timeslot). For example, there may be a group(s) of subframes where the firsttime slot includes a DM-RS transmission and another, possiblyoverlapping, group(s) of subframes where the second time slot includesDM-RS transmission. For example, a data stream may be characterized byan OFDM transmission schedule whereby a DM-RS transmission isincorporated into a single OFDM symbol of a first time slot of one ormore subframes (e.g., as shown in FIG. 3A) and is incorporated into asingle OFDM symbol of a second time slot of one or more subframes (e.g.,as shown in FIG. 3B). The subframe(s) of the data stream may alternatebetween subframe(s) that incorporate the DM-RS transmission in the firsttime slot and subframe(s) that incorporate the DM-RS transmission in thesecond time slot. The subframe(s) that incorporate the DM-RStransmission in the first time slot may be equal to, greater than, orless than the subframe(s) that incorporate the DM-RS transmission in thesecond time slot.

In an example, a WTRU may determine the identity of a time slot thatincludes (and/or does not include) a DM-RS transmission based on thephysical resource block(s) (PRB(s)) associated with an allocation.Therefore, the time slot used for DM-RS transmission may vary based onthe PRB. For example, there may be a set of PRBs within a subframe wherethe first time slot includes a DM-RS transmission in an appropriatesymbol of the first time slot. There may be a second set of PRBs,possibly overlapping the first set of PRBs, where the second time slotincludes a DM-RS transmission in an appropriate symbol of the secondtime slot.

In an example, the OFDM symbol used for DM-RS transmission may beshifted towards the edge of a time slot. For example, if DM-RS is to betransmitted solely in the first time slot, the last symbol of the firsttime slot may be used for DM-RS transmission. On the other hand, if theDM-RS is to be transmitted solely in the second time slot, the firstsymbol of the second time slot may be used for DM-RS transmission.

FIG. 4 is a diagram of an example mapping of DM-RS transmission that maybe shifted towards the edge of a time slot of a subframe with a normalcyclic prefix. As shown in FIG. 4, a subframe 400 may include two timeslots, a first time slot 402 and a second time slot 404, and a subframe410 may include two time slots, a first time slot 412 and a second timeslot 414. The subframe 410 may be a subsequent subframe (e.g., aconsecutive subframe) of the subframe 400. A DM-RS transmission 406 maybe included in the last OFDM symbol, such as the seventh OFDM symbol 408for normal cyclic prefix, of the first time slot 402 of the subframe400, and the DM-RS transmission 406 may be included in the first OFDMsymbol 418 of the second time slot 414 of the subframe 410. The DM-RStransmission 406 may be absent from the second time slot 404 of thesubframe 400 and absent from the first time slot 412 of the subframe410. For example, the OFDM symbols that do not include DM-RStransmission may include user data and/or control signaling as opposedto a DM-RS.

In an example, the groups may be such that certain subframes are notincluded in either group and therefore certain subframes may occurwithout any DM-RS transmission. If one or more subframes do not includea DM-RS, the network may be configured to utilize DM-RS subframebundling for channel estimation for those subframes. As a result, aDM-RS from another subframe may be used to estimate the channel for asubframe that does not include a DM-RS transmission. Thus, a singleDM-RS may be applicable to multiple subframes.

FIG. 5 is a diagram of an example mapping of DM-RS transmission in twosubframes using subframe bundling with a normal cyclic prefix. As shownin FIG. 5, a subframe 500 may include two time slots, a first time slot502 and a second time slot 504, and a subframe 510 may include two timeslots, a first time slot 512 and a second time slot 514. The subframe510 may be a subsequent subframe (e.g., a consecutive subframe) of thesubframe 500. A DM-RS transmission 506 may be included in an OFDMsymbol, such as the fourth OFDM symbol 508, of the first time slot 502of the subframe 500. The subframe 510 may not include a DM-RS of theDM-RS transmission 506. As such, the DM-RS transmission 506 of thesubframe 500 may be used to estimate the channel for the subframe 510.Thus, a single DM-RS (e.g., the DM-RS included in the fourth OFDM symbol508 of the subframe 500) may be applicable to multiple subframes (e.g.,the subframe 510). Although illustrated as being included in the fourthOFDM symbol 508 of the second time slot 504 of the subframe 500, theDM-RS transmission 506 may be included in any OFDM symbol of either timeslot 502, 504 of the subframe 500. Although illustrated as being usedfor a subsequent subframe, the DM-RS transmission 506 may be used toestimate the channel for a subframe that precedes the subframe 510.

In an example, a WTRU may be configured to utilize interlaced frequencydivision multiplexing (FDM) for DM-RS transmission. For example, a DM-RStransmission may be transmitted over a subset of subcarriers on anappropriate OFDM symbol (e.g., the fourth OFDM symbol for normal cyclicprefix, the third OFDM symbol for extended cyclic prefix, any other OFDMsymbol used for enhanced DM-RS, etc.). The subcarriers that are not partof the subset may be used for data user data transmission and/or othercontrol channel transmission (e.g., via the PUSCH and/or the PUCCH).

For example, a DM-RS may be interlaced with the PUSCH, PUCCH, and/or anyother UL channel. For example, half the subcarriers in a given OFDMsymbol may be used for DM-RS transmission, while the other half may beused for PUSCH. As an example, even numbered subcarriers in an OFDMsymbol may be used for DM-RS transmission (e.g., DM-RS data is mapped tothe REs that correspond to the even numbered subcarriers of the OFDMsymbol) while odd numbered subcarriers may be used for PUSCH and/orPUCCH (e.g., PUSCH data is mapped to the REs that correspond to the oddnumbered subcarriers with the OFDM symbol), or vice-versa.

In an example, half of the subcarriers typically utilized for DM-RStransmission in a given OFDM symbol (e.g., according to Release 8/10)may be used for DM-RS transmission, while the other half of the REs maybe used for other types of data transmission, for example, to reduceDM-RS overhead. In an example, greater or less than half of thesubcarriers typically utilized for DM-RS transmission in a given OFDMsymbol (e.g., according to Release 8/10) may be used for DM-RStransmission. For example, the total number of subcarriers used for agiven DM-RS transmission may be an integer that is less than the totalnumber of subcarriers assigned to the WTRU. In an example, the totalnumber of subcarriers used for DM-RS transmission may remain a multipleof 12, thus enabling the reuse of Zadoff Chu (ZC) sequences designed forlegacy DM-RS. Similarly, for the case where some PRBs include DM-RStransmissions and others do not, the number of PRBs that include a DM-RStransmission may be different than the number of PRBs that do notinclude a DM-RS transmission.

FIG. 6 is a diagram of an example mapping of DM-RS transmission in asubset of subcarriers of orthogonal frequency-division multiplexing(OFDM) symbols of two time slots of a subframe. As shown in FIG. 6, asubframe 600 may include two time slots, a first time slot 602 and asecond time slot 604 (e.g., which may be represented by a PRB, but arenot limited to such a size). An OFDM symbol in the time slots 602, 604may include a DM-RS transmission 620, but the DM-RS transmission 620 maybe included in a subset of the subcarriers of the OFDM symbols. Forexample, a subset of the subcarriers of a fourth OFDM symbol 606 of thefirst time slot 602 of the subframe 600 may include the DM-RStransmission 620, while the remaining subcarriers of the fourth OFDMsymbol 606 may include user data and/or control signaling. Statedanother way, one or more REs of a PRB of the fourth OFDM symbol 606 mayinclude DM-RSs while the remaining REs of the PRB may include user dataand/or control signaling. Similarly, a subset of the subcarriers of afourth OFDM symbol 608 of the second time slot 604 of the subframe 600may include the DM-RS transmission 620, while the remaining subcarriersof the fourth OFDM symbol 606 may include user data and/or controlsignaling. For example, odd numbered sub-carriers of the OFDM symbol 606and the OFDM symbol 608 may include the DM-RS transmission 620, whileeven numbered sub-carriers of the OFDM symbol 606 and the OFDM symbol608 may include user data and/or control signaling.

Although illustrated as being included in the fourth OFDM symbols 606,608 of the subframe 600, the DM-RS transmission 620 may be included inany OFDM symbol of either time slot 602, 604 of the subframe 600.Although illustrated as being included in the odd numbered sub-carriersof the OFDM symbol 606 and the OFDM symbol 608, the DM-RS transmission620 may be included in the even numbered sub-carriers of the OFDM symbol606 and the OFDM symbol 608, while user data and/or control signalingmay be included in the odd numbered sub-carriers of the OFDM symbol 606and the OFDM symbol 608. The OFDM symbol of the first time slot 602 thatincludes the DM-RS transmission 620 may be different (e.g., a differentposition) than the OFDM symbol of the second time slot 604 that includesthe DM-RS transmission 620. The number, order, and/or position of REsthat include the DM-RS transmission 620 may vary between time slots of asubframe, between subframes of a data stream, and/or between PRBsassociated with the DM-RS transmission 620.

In an example, the first six subcarriers of the appropriate OFDM symbolin a PRB may be used for DM-RS transmission, while the last sixsubcarriers may be used for transmission of user data and/or controlsignaling (e.g., via the PUSCH and/or the PUCCH), or vice-versa. FIG. 7is a diagram of an example mapping of DM-RS transmission in a subset ofsubcarriers of OFDM symbols of two time slots of a subframe. As shown inFIG. 7, the first six subcarriers of an OFDM symbol, such as the fourthOFDM symbol 706, of a PRB of a first time slot 702 may be used for DM-RStransmission 720, while the last six subcarriers of the PRB may be usedfor transmission of user data and/or control signaling (e.g., via thePUSCH and/or the PUCCH). Similarly, the first six subcarriers of an OFDMsymbol, such as the fourth OFDM symbol 708, of a PRB of a second timeslot 704 may be used for DM-RS transmission 720, while the last sixsubcarriers of the PRB may be used for transmission of user data and/orcontrol signaling (e.g., via the PUSCH and/or the PUCCH). Althoughillustrated as being included in the fourth OFDM symbols 706, 708 of thesubframe 700, the DM-RS transmission 720 may be included in any OFDMsymbol of either time slot 706, 708 of the subframe 700. In an example,the OFDM symbols may be different for the time slots 706, 708 of thesubframe 700.

In an example, for certain time slots and/or subframes, the subcarriersin a PRB (e.g., all of the subcarriers in a PRB) may be used for PUSCHand/or PUCCH transmission (e.g., the WTRU may refrain from transmittingDM-RS in the PRB). If a given PRB does not include DM-RS transmission,then a WTRU may be assigned a plurality of PRBs, where the plurality ofPRBs may be a combination of one or more PRBs that include a DM-RStransmission (e.g., in a subset of, or all, subcarriers) and one or morePRBs that do not include a DM-RS transmission. As such, a DM-RStransmission schedule may be characterized by one or more PRBs that donot include a DM-RS transmission and one or more PRBs that include theDM-RS transmission, whereby the PRBs that do include the DM-RStransmission may include the DM-RS transmission in one or moresubcarriers of one or more OFDM symbols of the PRB.

If interlaced FDM is utilized, the peak-to-average-power (PAPR) of theDM-RS portion of an OFDM symbol may be low due to ZC sequencegeneration. Similarly, the PAPR of the PUSCH portion of the OFDM symbolmay be low due to the use of discrete Fourier transform (DFT) precoding.However, if the DM-RS transmission and the PUSCH transmission aremultiplexed, it may be that the combination of the two signals (e.g., ofwhich each may be characterized by low PAPR) into a single symbol mayresult in a transmission that is no longer characterized by a low PAPR.In order to ensure the interlaced symbol retains low PAPRcharacteristics, a WTRU may be configured to power scale the PUSCH REsaccordingly. In an example, a WTRU may use a scaling factor to assist inthe demodulation of the scaled PUSCH in the interlaced OFDM symbol. Forexample, a WTRU may include a scaling value in its transmission toassist in the demodulation of the scaled PUSCH in the interlaced OFDMsymbol. In an example, a WTRU may be configured with approved scalingvalues that it may use in the event of an interlaced symbol losing itslow PAPR characteristics.

In an example, a combination of time and/or frequency multiplexingmethods may be used to decrease the number of resources utilized forDM-RS transmission. For example, in some embodiments a single time slotper subframe may be used for DM-RS transmission. The identity of thetime slot used for DM-RS transmission may depend on the PRB(s)associated with a given allocation. For example, a WTRU may beconfigured to utilize DM-RS transmission in the first timeslot of asubframe for a first subset of PRBs (e.g., odd numbered PRBs) andutilize DM-RS transmission in the second timeslot of a subframe for asecond subset of PRBs (e.g., even numbered PRBs). In an example, thenumber of PRBs with that include a DM-RS transmission may be greater,fewer, or equal to in number the number of PRBs that do not utilizeDM-RS transmission. In an example, a WTRU may be configured to utilizetwo (e.g., both) time slots of a subframe for DM-RS transmission for afirst subset of PRBs, to utilize a single (e.g., possibly alternating)time slot in a second subset of PRBs, and/or to refrain fromtransmitting DM-RSs in either timeslot for a third subset of PRBs.

In an example, a WTRU may use interleaving of PUSCH and/or PUCCHtransmissions and DM-RS transmission in both time slots and/or in eachPRB. As a result, a given subcarrier may have no DM-RS symbol mapped toit during a slot or subframe, a single DM-RS symbol mapped to it duringa slot or subframe, and/or two DM-RS symbols mapped to it during a slotor subframe. For example, for a given PRB, odd numbered subcarriers mayinclude a DM-RS transmission in the appropriate symbol of the first timeslot, while even numbered subcarriers may include a DM-RS transmissionin the appropriate symbol of the second time slot, or vice versa.

If interlaced frequency division multiplexing is used to decrease theDM-RS transmission overhead, the sequence (e.g., pilot sequence) usedfor DM-RS transmission may be modified. For example, the value of theDM-RS sequence mapped to a given resource element in a DM-RStransmission schedule may be the same value that would otherwise be usedin the legacy scheme in resource elements for which DM-RS is stilltransmitted. The same sequence and resource mapping as in the legacyscheme may be used, but with puncturing such that some resource elementsmay be replaced with PUSCH and/or PUCCH symbols according to a reductionscheme.

As another example, the DM-RS sequence may be calculated based on theactual number of symbols for resource elements available to the uplink(UL) DM-RS in a given time slot M_(SC) ^(RS), which may be smaller thanthe number of subcarriers in the PUSCH resource allocation M_(SC)^(PUSCH). If the total number of subcarriers used to transmit DM-RS inone time slot is a multiple of 12, a WTRU may reuse the sequencegeneration method utilized for legacy DM-RS transmission. A WTRU maydetermine the appropriate sequence length based on the number of PRBsgranted and/or the ratio of REs used for DM-RS transmission to totalREs. For example, in case of an interlaced frequency divisionmultiplexing scheme in which DM-RS symbols and PUSCH symbols areinterspersed within the same time slot, the reference signal sequencemay be calculated based on a formula, for example, except that M_(SC)^(RS)=M_(SC) ^(PUSCH)/2 (e.g., in case the DM-RS is reduced by a factorof two). The DM-RS to RE mapping may be pre-configured and/or may beperformed in an order similar to previous releases, although the WTRUmay be configured to skip certain subcarriers if the skipped subcarriersare not to be used for DM-RS transmission. The mapping to resourceelements may follow the same rules as a legacy scheme, e.g., by order ofsubcarrier first and time slot second, within the resource elementsdesignated for DM-RS.

For cases where the number of subcarriers used to transmit DM-RSs in onesymbol is not a multiple of 12, sequences (e.g., new sequences) may bedetermined that satisfy similar properties as ZC sequences.

For cases where a single OFDM symbol (e.g., and/or a single time slot)per subcarrier is used for DM-RS transmission, the identity of thesymbol (and/or time slot) used for DM-RS transmission may change overtime (e.g., as a function of slot number, subframe number, system framenumber (SFN), etc.) and/or over frequency (e.g., as a function ofsubcarrier number, as a function of PRB, etc.). The size of the sequenceM_(SC) ^(RS) may remain the same as M_(SC) ^(PUSCH). The mapping toresource elements may be modified, for example, such that it may be byorder of time slot first and subcarrier second. For the example casewhere DM-RS transmissions are included in even numbered subcarriers ofthe appropriate symbol of the first time slot and DM-RS transmissionsare included in odd numbered subcarriers in the appropriate symbol ofthe second time slot, the mapping of a single length 12*N ZC sequence(e.g., where N is the total number of PRBs) may be done sequentiallyover the subcarriers. Therefore, the first symbol of the ZC sequence maybe located in the first subcarrier in the first time slot. The secondsymbol of the ZC sequence may be located in the second subcarrier in thesecond time slot. The third symbol of the ZC sequence may be located inthe third subcarrier in the first time slot, and the fourth symbol ofthe ZC sequence may be located in the fourth subcarrier in the secondtime slot, and so on. Such a mapping approach may be applicable evenwhen groups of adjacent subcarriers have DM-RS transmission(s) in thesame time slot. For example, subcarriers 0,1,2 may have DM-RS data inthe first time slot, while subcarriers 3,4,5 may have DM-RS data in thesecond time slot, etc.

In an example, a WTRU may be configured to and/or triggered by thenetwork to utilize a certain type of DM-RS transmission schedule. Forexample, the WTRU may be triggered based on detecting and/or moving to asmall cell and/or a macro cell. The WTRU may be configured to utilize acertain DM-RS transmission schedule based on explicit signaling receivedfrom the network (e.g., radio resource control (RRC) signaling). Forexample, the network may configure the WTRU to devote greater or fewerresource elements for a DM-RS transmission and/or change the identity ofresource elements used for a DM-RS transmission. One or more of thefollowing methods for triggering the WTRU to change its DM-RStransmission schedule may be used in any combination.

In an example, higher layer signaling (e.g., medium access control (MAC)and/or RRC signaling) may semi-statically indicate the DM-RStransmission schedule to be used by a WTRU. In an example, a message mayuse a single bit to indicate whether to use a legacy (e.g., Release 8,Release 10, etc.) DM-RS transmission schedule or a DM-RS transmissionschedule characterized by reduced overhead (e.g., via a reduction inDM-RS). The DM-RS transmission schedule characterized by reducedoverhead may be a schedule that reduces the number of REs used for DM-RStransmission(s). The parameters for the DM-RS transmission schedulecharacterized by reduced overhead may be tied or linked to the cellphysical cell identifier (PCI). For example, small cells may beassociated with PCIs linked to DM-RS schedules characterized by reducedoverhead and macro cells may be associated with PCIs linked to legacyDM-RS transmission schedules.

Higher layer signaling may indicate a DM-RS transmission schedule (e.g.,whether a reduced DM-transmission schedule is to be used, an indicationof the identity of slots and/or subcarriers to use for DM-RStransmission, etc.). In an example, RRC may be utilized to provide aplurality of DM-RS transmission schedules, for example a normal DM-RStransmission schedule and a resource-saving DM-RS transmission schedule.Dynamic signaling (e.g., Layer 1 (L1) signaling such as grants receivedvia the physical downlink control channel (PDCCH), PDCCH orders, and/orMAC control elements (CEs)) may be used to indicate the DM-RStransmission schedule to use, for example, per UL transmission.

If a DM-RS transmission schedule characterized by reduced overhead is tobe indicated dynamically (e.g., by sending an indication of apre-configured DM-RS parameter set to be used), the configuration may beperformed in a variety of ways. For example, downlink controlinformation (DCI) included in a UL grant (e.g., DCI Format 0, DCI Format4, a new DCI Format, etc.) may include a bit(s) (e.g., a new bit(s)) toindicate the identity of the pre-configured set of parameters to beused. In an example, the configuration of a DM-RS transmission schedulecharacterized by reduced overhead may be implicitly linked or tied to aPCI and/or virtual cell identifier (VCID), and for example, may beimplicitly indicated by a VCID configuration.

In an example, a DM-RS transmission schedule may be implicitly indicatedby based on the properties or parameters associated with an uplinkgrant. For example, the WTRU may be configured to determine theappropriate DM-RS transmission schedule based on one or more of theallocation size, the Modulation Coding Scheme (MCS) level, the subframenumber, the frame number, the transmission mode, whether the grant isassociated with semi-persistent scheduling (SPS) or not, and/or thelike. In an example, a DCI Format (e.g., a new DCI Format) may bedesigned to be used with a specific set of DM-RS transmissionschedule(s). In an example, the appropriate DM-RS transmission schedulemay be linked or tied to whether the UL grant was received inWTRU-specific search space or the common search space within the PDCCH.In an example, a DM-RS transmission schedule(s) may be tied or linked tocertain component carriers. Therefore, a WTRU may be implicitlytriggered to utilize a DM-RS transmission schedule based on the carrierindicator field (CIF) include in an UL grant.

A WTRU may be configured to transmit PUSCH and/or PUCCH (e.g., and/orsome other UL channel and/or signal) and a DM-RS transmission on thesame set of resource elements and/or symbols. For example, DM-RStransmissions and PUSCH transmissions may occupy the same resources inthe time domain (e.g., REs within an OFDM symbol may include both DM-RStransmission data and PUSCH transmission data), in the frequency domain(e.g., REs within a subcarrier and/or PRB may include both DM-RStransmission data and PUSCH transmission data), and/or in both the timeand frequency domains (e.g., REs may include both DM-RS transmissiondata and PUSCH transmission data, for example on different transmissionlayers, separated by different cover codes, etc.). If DM-RStransmissions and PUSCH transmissions are to occupy the same resources,a WTRU may allocate half its transmission power to DM-RS transmissionand half to PUSCH transmission (e.g., or to transmission of other ULchannel(s) and/or signal(s)).

To facilitate demodulation, a WTRU may be configured to utilizeorthogonal cover codes (OCCs) to allow for the separation of the DM-RStransmission from the PUSCH transmission, for example if thetransmissions are to occupy the same REs. For example, a WTRU may beconfigured to repeat the same data symbols (e.g., PUSCH transmission) inthe two time symbols that are used for DM-RS. Use of appropriate OCCprecoding for DM-RS symbols (e.g., [1 1]) and/or PUSCH symbols (e.g.,[1-1]) may allow for proper demodulation at the eNB. Such a codingtechnique may be used in conjunction with examples of DM-RS transmissionschedules described herein.

In an example where PUSCH (e.g., and/or PUCCH) and DM-RS transmissioncollide (e.g., where a single symbol per subframe is used for DM-RStransmission, etc.), the PUSCH data to be mapped to REs that collidewith the DM-RS transmission(s) may be duplicated on other REs collidingwith DM-RS, for example in the same symbol. For example, PUSCH data thatis to be mapped to REs used for DM-RS transmission may be transmitted onone or more additional REs (e.g., so at least two REs include a copy ofthe relevant PUSCH data) in order to increase the likelihood ofsuccessful reception. For example, if PUSCH data is duplicated acrosstwo REs when it is transmitted with a DM-RS transmission, the same DM-RStransmission may also be duplicated in those same RE pairs. If such anapproach is utilized, the OCC may be applied over subcarriers ratherthan over symbols. For example, data of a DM-RS transmission may bemapped to symbol 4 of the first time slot and in subcarriers 0, 2, 4, 6,8, 10. In such a case, the PUSCH in subcarriers 0, 2, and 4 may beduplicated in subcarriers 6, 8, and 10. Furthermore, the DM-RS datatransmitted on subcarriers 0, 2, and 4 may be duplicated in subcarriers6, 8, and 10. If an OCC of values [a b] is used for PUSCH transmissionand an OCC of values [c d] is used for DM-RS transmission, the values ofa, b, c, and/or d may be selected to facilitate the code multiplexing.For example, the PUSCH transmission in subcarriers 0, 2, and 4 may bemultiplied by ‘a’, while the PUSCH transmission in subcarriers 6, 8, and10 may be multiplied by ‘b’. The DM-RS transmission in subcarriers 0, 2,and 4 may be multiplied by ‘c’, and the DM-RS transmission insubcarriers 6, 8, and 10 may be multiplied by ‘d’.

In an example, a WTRU may be configured to interlace PUSCH transmissions(e.g., and/or PUCCH transmissions) with DM-RS transmissions usingreserved tones. For example, if PUSCH or other data is interlaced withDM-RS transmissions over different subcarriers within one symbol, thePUSCH data may be produced as an output of a DFT to reduce PAPR, and theDM-RS transmission may be a ZC sequence to also reduce the PAPR.Interlacing the DM-RS transmission and the PUSCH transmission into onetime symbol may affect the PAPR properties of the overall symbol. In anexample, to decrease the largest peaks of the overall OFDM signal, tonereservation may be used. For example, in one OFDM symbol (e.g., thefourth symbol of the first time slot, for normal cyclic prefix) somesubcarriers may be used for DM-RS transmission, other subcarriers may beused for PUSCH transmission, and other subcarriers may be used forreserved tones. The reserved tones may be modulated in such a way thatthe largest peaks of the overall OFDM signal may be suppressed, whichmay allow for reduced power-amplifier back-off.

As an example, a WTRU may be configured with a spacing of threesubcarriers between DM-RS transmission REs, PUSCH transmission REs(e.g., and/or PUCCH transmission REs), and reserved tone REs. Adifferent subcarrier shift may be applicable to one or more of the DM-RStransmission, the PUSCH transmission, and the reserved tonetransmission, for example to ensure the transmissions do not collide.For example, the DM-RS transmission may be mapped to a first subset ofsubcarrier (e.g., subcarriers 0, 3, 6, 9) of the appropriate OFDMsymbol, the PUSCH transmission may be mapped to a second subset ofsubcarriers (e.g., subcarriers 1, 4, 7, 10) of the same OFDM symbol, andthe remaining subcarriers (e.g., 2, 5, 8, 11) may be reserved for tonesconfigured to decrease the larger peaks of the OFDM signal.

In an example, one or more of the DM-RS transmission, the PUSCHtransmission, and the transmission of the reserved tones may beconfigured to use some or all subcarriers of respective (e.g., possiblyoverlapping) sets of PRBs, for example, one or more of the subcarrierswithin one PRB. In an example, the total number of REs used for DM-RStransmission, the total number of REs used for PUSCH transmission,and/or the total number of REs used for reserved tone transmission maybe OFDM symbol specific and/or PRB specific and/or the ratio of REs usedfor the different purposes may vary over time and/or frequency. Forexample, a WTRU may be configured with RE subsets to use for DM-RStransmission, PUSCH transmission, and/or reserved tone transmission. Thesubsets may be configured explicitly using a bitmap and/or a bitstreammapped to a table of possible RE subsets. In an example, a RE subset(e.g., for DM-RS transmission, PUSCH transmission, and/or reserved tonetransmission) may be obtained from configuration parameters. Suchconfiguration parameters may include the RE periodicity and/or asubcarrier shift.

In an example, a WTRU may be configured to precode one or more referencesignals (e.g., DM-RSs) with user data (e.g., PUSCH data). SC-FDMA may beused to minimize the PAPR, for example, in UL transmissions for LTE. Inan example, interlaced PUSCH and DM-RS symbols may be input to anSC-FDMA signal generator, for example, to decrease the overheadassociated with DM-RS transmission while maintaining a relatively lowPAPR. The bit stream that forms the input to the SC-FDMA signalgenerator may include alternating PUSCH and DM-RS modulation symbols. Inan example, the bit stream that forms the input to the SC-FDMA signalgenerator may include the DM-RS modulation symbols to be transmitted(e.g., in an OFDM symbol, slot, subframe, etc.) followed by the PUSCHmodulation symbols to be transmitted (e.g., or vice versa). The outputof the DFT may be applied to the appropriate OFDM symbol (e.g., thefourth symbol of the first and/or second time slot for normal cyclicprefix). In such a case, the RS may be different that a ZC sequence. Forexample, a Gold sequence initialized based on the cell PCI and/or theVCID may be used.

In order to decrease the DM-RS overhead, a WTRU may be configured toperform UL transmission(s) without DM-RS transmission. To compensate forthe lack of DM-RSs, a WTRU may be configured to transmit precodedsounding reference signals (SRSs) and/or non-precoded SRSs in thesubframe where DM-RS-free PUSCH transmission occurs. Precoding of theSRSs may be omitted, for example, given that in LTE the uplink precodermatrix may be selected by the network and/or may be provided to the WTRUin an uplink scheduling grant.

To configure a WTRU for DM-RS-free transmission(s), the SRS requestfield may be used to indicate that the WTRU should perform DM-RS-freetransmission. For example, a WTRU may be configured such that one of theSRS parameter sets configured by higher layers for the SRS requestcorresponds to DM-RS-free PUSCH transmission with SRS. For example, anSRS request field value of ‘11’ may configure a WTRU to transmitaperiodic SRS with a DM-RS-free PUSCH. In an example, to configure aWTRU with DM-RS-free PUSCH, the network may use one of the reserved bitfields used for UL precoding information in DCI Format 4 and/or otherDCI Formats. The bits corresponding to the UL precoding informationfields may indicate a specific precoder matrix as well as the use ofDM-RS-free PUSCH transmission. As an example, for the case of twoantenna ports with one codeword, bit fields 6 and 7 may be used for onelayer DM-RS-free transmission with Transmitted Precoding MatrixIndicator (TPMI)=0 and TPMI=1 (e.g., or any other higher layerconfigured and/or pre-configured TPMI values), respectively. For twoantenna ports with two codewords, bit field 1 may be used to indicatetwo layer DM-RS-free transmission with TPMI=0. For four antenna portswith one codeword, bit fields 40-63 may be reused for one or two layerDM-RS-free transmission with a subset of available TPMI (e.g., eitherpre-configured or configured by higher layers). For four antenna portswith two codewords, bit fields 29-63 may be reused for two, three,and/or four layer DM-RS-free transmission with any of the available TPMI(e.g., either pre-configured and/or configured by higher layersignaling).

In an example, a WTRU may be able to transmit UL data using any of anumber of DM-RS transmission schedules, which for example, may include alegacy DM-RS transmission schedule(s) and/or one or more reduced DM-RStransmission schedule(s). In one or more subframes, a WTRU may use alegacy DM-RS transmission schedule, while in another subset of subframesthe WTRU may transmit DM-RS in a single time slot of a subframe. TheWTRU may be semi-statically configured with subsets of subframes, e.g.,via RRC signaling, where for one or more of the subset of subframes, theWTRU may use a different DM-RS transmission schedule. For example, twoor more DM-RS transmission schedules may be defined, where in a firstDM-RS transmission schedule the DM-RS is transmitted in a first slot andin a second DM-RS transmission schedule the DM-RS is transmitted in asecond slot. The WTRU may transmit the first DM-RS transmission schedulein even subframes and the second DM-RS transmission schedule in oddsubframes, for example, to enhance the quality of channel estimationwhen two UL transmissions occur in consecutive subframes. In an example,the WTRU may be configured via higher level signaling with one or moreof DM-RS transmission schedules, for example, with an index (e.g., eachwith an index). The WTRU may be configured (e.g., dynamically) with theappropriate DM-RS transmission schedule for a subframe (e.g., eachsubframe) by adding a corresponding index in the UL grant DCI. In anexample, a WTRU may be configured with a legacy DM-RS transmissionschedule(s) as well as a DM-RS transmission schedule(s) characterized byreduced overhead. One or more bits may be included in a UL grant and maybe used to trigger a DM-RS transmission schedule(s). The absence of thebit and/or a predetermined value of the bit (e.g., 0 or 1) may cause aWTRU to use a legacy DM-RS transmission schedule.

There may be rules for switching DM-RS transmission schedules. The WTRUmay be configured to switch (e.g., dynamically switch) between differentDM-RS transmission schedules. For example, subframes where HARQ-ACK, RI,and/or CQI/PMI are transmitted in the PUSCH may use a first DM-RStransmission schedule. Whereas subframes where data (e.g., only data) istransmitted may use a second DM-RS transmission schedule. The DM-RStransmission schedule may be determined (e.g., implicitly) based on thenumber of transmission layers. The DM-RS transmission schedule may bedetermined (e.g., implicitly) based on the OCC used on the DM-RS. TheDM-RS transmission schedule may be determined (e.g., implicitly) basedon the virtual cell ID used for DM-RS. The DM-RS transmission schedulemay be determined (e.g., implicitly) based on the sequence and/or cyclicshift used for DM-RS.

The DM-RS transmission schedule to be used may be a function of theframe, subframe, and/or time slot number. A WTRU may be configured withsets of subframes for a (e.g., each) DM-RS transmission schedule, forexample, for semi-persistent scheduling. The WTRU may determine theDM-RS transmission schedule based on a previously used DM-RStransmission schedule. For example, if a first subframe uses a firstDM-RS transmission schedule, the next scheduled subframe may switch to adifferent DM-RS transmission schedule, for example, in a pre-configuredorder. The WTRU may be configured to switch DM-RS transmission schedulesfor each retransmission, for example, in a pre-configured order.

The DCI may be used to determine the DM-RS transmission schedule to beused in the scheduled grant. The DCI Format used may configure the WTRUfor a DM-RS transmission schedule. Values of the precoding informationfield in the DCI may indicate to the WTRU what DM-RS transmissionschedule to use. A WTRU may be configured to use different DM-RStransmission schedule based on the number of layers. Upon decoding anuplink grant for a specific number of layers, the WTRU may determine theappropriate DM-RS transmission schedule.

In an example, a transport block size may be indicated. In a subframe inwhich the WTRU uses a DM-RS transmission schedule characterized byreduced overhead, the transport block size determination may bedifferent from a case in which a WTRU uses a legacy DM-RS transmissionschedule. The modulation and coding scheme (MCS) indication included inthe UL grant may have a different mapping to Transport Block Sizes(TBS). A WTRU may be configured with a MCS to TBS mapping table (e.g., anew MCS to TBS mapping table) for DM-RS subframes. The table may takeinto account the reduction in DM-RS overhead. A WTRU may use the DM-RStransmission schedule, which may have been obtained semi-statically ordynamically, to determine the appropriate MCS-to-TBS mapping table touse.

In another example, the MCS index included in the UL grant mayimplicitly indicate the TBS table that may be used. The WTRU maydetermine the type of DM-RS transmission schedule that may be used basedon the MCS index. A subset of MCS indices may be associated with a DM-RSsubframe type. The WTRU may be configured via higher layers, the mappingbetween values of MCS, and/or the type of DM-RS. For example, a WTRU maybe configured with a list of MCS indices. Such MCS indices may map to aDM-RS transmission schedule(s) (e.g., a DM-RS transmission schedulecharacterized by reduced overhead), and other MCS indices may map toDM-RS transmission schedule(s) (e.g., legacy DM-RS transmissionschedule(s)).

An MCS-to-TBS table that may be used for DM-RS transmission schedule(s)may be defined explicitly and preconfigured in the WTRU. In an example,the TBS value may be determined as a function of the legacy MCS-to-TBStable. For example, if the DM-RS transmission schedule(s) characterizedby reduced overhead are obtained by transmitting DM-RS in one time slot,the overhead reduction may be 12 REs per PRB (e.g., a reduction of1/14). Upon receiving an MCS index, the WTRU may determine the TBS byexamining the table configured for a legacy DM-RS transmission scheduleand multiplying the TBS value by a preconfigured value, e.g.,156/144≈1.0833 and using a floor function, e.g.,TBS_(enhanced)=└1.0833TBS┘, where TBS may be obtained from the MCSvalue. In an example, given that the savings in overhead from DM-RSlocated in a single time slot are equivalent to a gain of an extra PRBevery 14 PRBs, the conversion may be performed taking those savings intoaccount. For example, every 14 PRBs assigned may map to a TBS for 15PRBs. An adjustment may be added for assignments that are not multiplesof 14. The TBS may be determined from the MCS and the number of PRBsallocated such that, for example,TBS_(enhanced)=ƒ(I_(MCS),N_(PRB)+└N_(PRB)/14┘)+Δ mod(N_(PRB), 14), wherethe function ƒ may be the appropriate location on the preconfiguredmapping table and delta is a preconfigured value.

In an example, DM-RS transmission schedule(s) may be configured forretransmission of PUSCH. The WTRU may support the use of multiple DM-RStransmission schedules. The type of DM-RS transmission schedule maychange often. This change may occur after a WTRU has made atransmission, but before the WTRU makes a retransmission. Accordingly,the type of DM-RS transmission schedule a WTRU is expected to use inthis situation may be ambiguous. In an example, when a WTRU is indicatedvia a NACK on PHICH that the WTRU should retransmit the transport block,it may be assumed that the WTRU reuses the same DM-RS transmissionschedule that was used in the previous transmission, overriding a DM-RStransmission schedule for that subframe.

In another example, a WTRU may be provided an UL grant on a PDCCH thatrequested a retransmission, e.g., by an appropriate toggle of a dataindicator. The WTRU may be indicated via the MCS index the redundancyversion that it is expected to transmit. The MCS indices mapping todifferent redundancy versions may be separated into different groups.One or more of the group(s) (e.g., each group) may map to a differentDM-RS transmission schedule. The WTRU may be able to infer or determinethe appropriate MCS/TBS to use in the retransmission, for example, fromthis mapping, as well as the appropriate redundancy version.

In an example, the WTRU may use a combination of the configured DM-RStransmission schedule for the retransmission subframe and the signaledredundancy version to determine the appropriate MCS/TBS to use for theretransmission. One or more of the MCS indices (e.g., each MCS index)that is mapped to redundancy versions may have multiple meanings,depending on the configured DM-RS transmission schedule for theretransmission subframe.

In an example, for an UL grant indicating retransmission, the WTRU maybe provided with a MCS index (e.g., a new MCS index) that is not mappedto a redundancy version. The presence of this MCS index may implicitlyindicate to the WTRU that a DM-RS transmission schedule (e.g., a DM-RStransmission schedule characterized by reduced overhead) may be used inthe retransmission subframe. It may indicate to the WTRU the MCS/TBS touse, for example, using the appropriate TBS mapping rule based on theDM-RS transmission schedule. To allow for different redundancy versions,the WTRU may be preconfigured with an order of redundancy and versionsto be used when the DM-RS transmission schedule changes and the MCS isnot used for redundancy version indication.

In an example, in an UL grant for retransmission, a bit flag may beincluded that may indicate the type of DM-RS transmission schedule thatmay be used. This indication (e.g., in combination with the MCS index,which may trigger a redundancy version) may allow the WTRU to determinethe redundancy version as well as the appropriate MCS/TBS.

One or more embodiments contemplate DM-RS sequence generation.Embodiments recognize that the sequence-group number that may be usedfor DM-RS sequence generation (e.g., the determination of a DM-RStransmission schedule(s)) may no longer be a function of the time slot,perhaps given that there may be a single DM-RS per subframe, among otherreasons. In some embodiments, the sequence-group number u may be definedas u=(f_(gh)(n)+f_(ss))mod 30, where n=i−1 for the i^(th) DM-RStransmission in the radio frame, for example, for reduced DM-RStransmission schedule(s) among other reasons. For example, a WTRU may beconfigured with a radio frame where one or more, or each, subframe mayhave a single DM-RS located in the first time slot, the n could bedefined as n=SFNmod10, where SFN is the subframe number. The value of nmay be reused, for example, to replace the slot number in a legacyformulation of sequence hopping and/or cyclic shift hopping, among otherreasons.

The sequence-group hopping, sequence hopping, and/or cyclic shifthopping may be performed over subframes and/or the hopping values mayremain constant over pairs of time slots, for example, for a DM-RStransmission schedule where a sequence (e.g., a single sequence) may bespread over multiple symbols (e.g., the hybrid method where a singleDM-RS is partially in a first time slot and partially in the second timeslot), among other scenarios.

The WTRU may be indicated (e.g., explicitly indicated) what value of nmay be used in the UL grant. Sequence-group hopping, sequence hopping,and/or cyclic-shift hopping may be re-initiated, for example, uponswitching from one DM-RS transmission schedule to another, among otherscenarios.

Data and/or control information may be multiplexed. A number of codedmodulation symbols per layer for HARQ-ACK, RI, PMI/CQI, and/or UL-SCHdata may be used. In some subframes, data may be multiplexed with CQI,PMI, RI and/or ACK. In such scenarios, the mapping of one or more, oreach, component of the transport block may be done according to one ormore of the rules described herein, for example, in order to properlytake account of a reduced DM-RS transmission schedule(s), among otherreasons. For example, when the WTRU transmits HARQ-ACK bits, and/or rankindicator bits, and/or CQI/PMI bits, among other scenarios, it maydetermine the number of coded modulation symbols per layer Q′ forHARQ-ACK, and/or rank indicator, and/or CQI/PMI as a function ofN_(symb) ^(PUSCH-initial), M_(SC) ^(PUSCH) and/or M_(SC)^(PUSCH-initial), where N_(symb) ^(PUSCH-initial)=(2(N_(symb)^(UL)−1)−N_(SRS)). N_(symb) ^(UL) is the number of SC-FDMA symbols persubframe. N_(SRS) is either 0 or 1, perhaps depending on if there is anSRS transmission in the subframe, among other reasons. M_(SC) ^(PUSCH)is the scheduled bandwidth for PUSCH transmission in the currentsubframe. M_(SC) ^(PUSCH-intial) is the initial scheduled bandwidthobtained from the initial (E)PDCCH.

In some embodiments, perhaps if the WTRU is scheduled with a reducedDM-RS transmission schedule, and perhaps where there may be a singleDM-RS symbol per subframe, among other scenarios, the WTRU may beconfigured to use N_(symb) ^(PUSCH-initial)=(2(N_(symb)−1)−N_(SRS)+1).In some embodiments, perhaps for a legacy DM-RS transmission schedule,among other scenarios, the product of N_(symb) ^(PUSCH-initial), M_(SC)^(PUSCH-initial) may be used in a function to determine Q′ and/or G, thetotal number of coded bits for UL-SCH data information. In someembodiments, perhaps for a reduced DM-RS transmission schedule, amongother scenarios, the product N_(symb) ^(PUSCH-initial). M_(SC)^(PUSCH-initial) in the function for Q′ and G, may be replaced by(N_(symb) ^(UL)−N_(SRS)). M_(SC) ^(PUSCH-initial)−N_(ULDM-RS), whereN_(ULDM-RS) is the total number of REs that may be used for a DM-RStransmission schedule in the scheduled bandwidth.

In some embodiments, perhaps for a reduced DM-RS transmission schedule,among other scenarios, there may be a set of values of PUSCHtransmission offsets (e.g., new values and/or heretofore undefined),β_(offset) ^(HARQ-ACK), β_(offset) ^(RI) and/or β_(offset) ^(CQI),possibly configured via higher layers, for example. The relationshipbetween the higher layer signaled indices and the offsets may depend onwhether the transmission in that subframe is for a DM-RS transmissionschedule, among other factors.

Embodiments contemplate a channel interleaver of UL-SCH data, ACK-NACK,RI, and/or CQI/PMI. A channel interleaver may implement a time-firstmapping of modulation symbols onto the transmit waveform. Theinterleaver may be done by filling a matrix with N_(symb) ^(PUSCH)columns and/or the number of rows that may be used to transmit at leastsome, or all, the data concatenated with CQI/PMI. In some embodiments,perhaps when configured with a reduced DM-RS transmission schedule,among other scenarios, the number of columns of the matrix may bedetermined by using N_(symb) ^(PUSCH)=(2(N_(symb) ^(UL)−1)−N_(SRS)+1).In some embodiments, the WTRU may use N_(symb) ^(PUSCH)=(2N_(symb)^(UL)−N_(SRS)) and may ensure that when data, HARQ-ACK, RI, and/orCQI/PMI information is written into the matrix, among other scenarios,the WTRU may skip one or more matrix entries that may be occupied byblank values. These blank values may be used to insert a reduced DM-RS.

There may be column sets for the insertion of HARQ-ACK and/or RIsymbols. These column sets may ensure that HARQ-ACK and/or RI may be asclose as possible to DM-RS. The column sets may be modified for the useof a reduced DM-RS transmission schedule. In some embodiments, perhapsfor a single DM-RS per subframe, and perhaps located in a single timeslot, among other scenarios, the HARQ-ACK and/or RI may be located(e.g., solely located) in the slot with DM-RS. In some embodiments, thesymbol(s) for HARQ-ACK may be the one or two symbols (or more) closestto the DM-RS symbol and the symbol(s) for the RI may be the next one ortwo symbols (or more) closest to the DM-RS. For example, for DM-RS insymbol x of a subframe, the HARQ-ACK may be transmitted in symbols x−1and x+1 and the RI may be transmitted in symbols x−2 and x+2. In someembodiments, the WTRU may be configured to use one or more symbols forthe HARQ-ACK and/or RI. In some embodiments, perhaps for an DM-RS insymbol x of a subframe, among other scenarios, the HARQ-ACK may belocated in symbols x−2, x−1, x+1, x+2 and/or the RI may be located insymbols x−4, x−3, x+3, x+4. In some embodiments, the HARQ-ACK may belocated in symbols x−3, x−1, x+1, x+3 and/or the RI may be located insymbols x−4, x−2, x+2, x+4. In some embodiments, perhaps given that theDM-RS may be located near the beginning or end of a subframe, amongother factors, there may not be enough symbols on one or more, or both,sides to accommodate using multiple symbols for HARQ-ACK and/or RI. Insome embodiments, the symmetry constraint may be removed. For example,for an DM-RS in symbol 3, the HARQ-ACK may be located in symbols 2, 4and 5 and/or the RI may be located in symbols 1, 6 and 7. As anotherexample, the HARQ-ACK may be located in symbols 2, 4 and 6 and/or the RImay be located in symbols 1, 5 and 7.

Embodiments contemplate modified Orthogonal Cover Code (OCC) for a DM-RStransmission schedule. The use of orthogonal cover codes on the DM-RSmay enable an increase in number of layers that can be supported and/orthe ability to perform MU-MIMO. One or more embodiments contemplate thatit may be useful to modify OCC behavior where a reduced DM-RS may beused, among other scenarios, for example. A DM-RS transmission schedulemay be used to use one or more orthogonal cover codes (OCC) on a DM-RS,for example, to enable MU-MIMO. A DM-RS transmission schedule may beused to provide uplink control information (UCI) on the PUSCH, forexample, with reduced DM-RS.

A DM-RS transmission schedule may be repeated over one or more pairs ofsubcarriers. A DM-RS transmission schedule may be repeated over xsubcarriers. This repetition can be over multiple SC-FDMA symbols. Forexample, in a solution where DM-RS is transmitted in a single SC-FDMAsymbol, the first x subcarriers may transmit a first symbol of thesequence, the second x subcarriers may transmit a second symbol of thesequence, and so on. This may be repeated for one or more, or each,transmission layer, whereby one, or more, or each, layer may bemultiplexed on the same REs. In an example where the DM-RS may be in afirst SC-FDMA symbol for one set of subcarriers and may be in a secondSC-FDMA symbol for another (e.g., possibly disjoint) set of subcarriers,the sequence may be repeated such that one or more, or every, symbol inthe sequence may occur once or more in the first SC-FDMA symbol and/oronce or more in the second SC-FDMA symbol, on another subcarrier. Forexample, the DM-RS may be located in even subcarriers of SC-FDMA symbol3 and in odd subcarriers of SC-FDMA symbol 10. The first layer's DM-RSsequence may be denoted by [a b c d e . . . ]. In such scenarios, thesymbol ‘a’ may be placed in subcarrier 0 of SC-FDMA symbol 3 and/orsubcarrier 1 of SC-FMDA symbol 10. Symbol ‘b’ may be placed insubcarrier 2 of SC-FDMA symbol 3 and/or subcarrier 3 of SC-FDMA symbol10, and so on. This may be repeated for one or more other DM-RS layers,whereby one or more, or each, layer may be multiplexed on the same REs.

In some embodiments, perhaps in order to allow for the properdemodulation of one or more, or each transmission layer, among otherreasons, OCC may be used in conjunction with cyclic shifts of the DM-RStransmission schedule. In some embodiments, perhaps where the DM-RS maybe repeated in multiple subcarriers (e.g., whether on the same SC-FDMAsymbol or not), among other scenarios, a different OCC vector per layercan be applied over multiple subcarriers. For example, a first OCCvector ‘y’ can be applied on one layer of DM-RS sequence symbols andanother OCC vector ‘z’ can be applied on another layer.

In some embodiments, perhaps where DM-RS may be transmitted on a singleSC-FDMA symbol and/or the DM-RS sequence symbols may be repeated over xsubcarriers, among other scenarios, one or more, or each, OCC vector mayalso be of length x and/or the OCC can be applied as described herein.For example, for a first layer, one or more, or each, set of xsubcarriers carrying the first sequence of DM-RS may be multiplied by‘y’. For a second layer, one or more, or each, set of x subcarrierscarrying the second sequence of DM-RS may be multiplied by ‘z’.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element can be used alone or in any combination with theother features and elements. In addition, the methods described hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable medium for execution by a computeror processor. Examples of computer-readable media include electronicsignals (transmitted over wired or wireless connections) andcomputer-readable storage media. Examples of computer-readable storagemedia include, but are not limited to, a read only memory (ROM), arandom access memory (RAM), a register, cache memory, semiconductormemory devices, magnetic media such as internal hard disks and removabledisks, magneto-optical media, and optical media such as CD-ROM disks,and digital versatile disks (DVDs). A processor in association withsoftware may be used to implement a radio frequency transceiver for usein a WTRU, UE, terminal, base station, RNC, or any host computer.

1. A method comprising: selecting a demodulation reference signal (DM-RS) transmission schedule out of a plurality of DM-RS transmission schedules, wherein the plurality of DM-RS transmission schedules comprises a DM-RS transmission schedule characterized by DM-RS transmission being mapped to at least one orthogonal frequency-division multiplexing (OFDM) symbol in each time-slot of a subframe of a data stream, and wherein the selected DM-RS transmission schedule is characterized by DM-RS transmission being mapped to a single OFDM symbol of a subframe of a data stream; and transmitting the data stream according to the selected DM-RS transmission schedule.
 2. The method of claim 1, wherein the OFDM symbol is associated with a first time slot of the subframe and the selected DM-RS transmission schedule is further characterized by Physical Uplink Shared Channel (PUSCH) transmission or Physical Uplink Control Channel (PUCCH) control information being mapped to a corresponding OFDM symbol of a second time slot of the subframe of the data stream.
 3. The method of claim 1, wherein the OFDM symbol of the selected DM-RS transmissions schedule is associated with a second time slot of the subframe and the selected DM-RS transmission schedule is further characterized by Physical Uplink Shared Channel (PUSCH) transmission or Physical Uplink Control Channel (PUCCH) control information being mapped to a corresponding OFDM symbol of a first time slot of the subframe of the data stream.
 4. The method of claim 1, wherein the OFDM symbol of the selected DM-RS transmissions schedule is a last OFDM symbol of a first time slot of the subframe or the OFDM symbol is a first OFDM symbol of a second time slot of the subframe.
 5. The method of claim 1, wherein the selected DM-RS transmission schedule is further characterized by the DM-RS transmission being mapped to a first OFDM symbol of a first time slot of a first subframe of the data stream and a second OFDM symbol of a second time slot of a second subframe of the data stream.
 6. The method of claim 1, wherein the selected DM-RS transmission schedule is further characterized by the DM-RS transmission being mapped to a first subset of subcarriers of the OFDM symbol and Physical Uplink Shared Channel (PUSCH) transmission or Physical Uplink Control Channel (PUCCH) control information being mapped to a second set of subcarriers of the OFDM symbol, wherein the first set of subcarriers is different than the second set of subcarriers.
 7. The method of claim 1, wherein the data stream comprises Physical Uplink Shared Channel (PUSCH) transmission or Physical Uplink Control Channel (PUCCH) control information.
 8. The method of claim 1, wherein the method is performed by a wireless transmit/receive unit (WTRU), and wherein selecting the DM-RS transmission schedule is based on whether the WTRU is connected to a small cell or connected to a macro cell.
 9. (canceled)
 10. A method comprising: determining to use a demodulation reference signal (DM-RS) transmission schedule out of a plurality of DM-RS transmission schedules, wherein the DM-RS transmission schedule is characterized by a DM-RS transmission being mapped to a first subset of subcarriers of an orthogonal frequency-division multiplexing (OFDM) symbol of a subframe of a data stream and Physical Uplink Shared Channel (PUSCH) transmission or Physical Uplink Control Channel (PUCCH) control information being mapped to a second set of subcarriers of the OFDM symbol, wherein the first set of subcarriers is different than the second set of subcarriers; and transmitting the data stream according to the DM-RS transmission schedule.
 11. The method of claim 11, wherein the first subset of the subcarriers of the OFDM symbol is half of the total subcarriers of the OFDM symbol.
 12. The method of claim 11, wherein the first subset of subcarriers of the OFDM symbol is the first six subcarriers of a physical resource block of the OFDM symbol or the last six subcarriers of a physical resource block of the OFDM symbol.
 13. The method of claim 11, wherein the first subset of the subcarriers of the OFDM symbol is an integer multiple of twelve.
 14. The method of claim 11, wherein the first subset of subcarriers is even numbered subcarriers and the second subset of subcarriers is odd numbered subcarriers or the first subset of subcarriers is odd numbered subcarriers and the second subset of subcarriers is even numbered subcarriers.
 15. The method of claim 11, wherein the data stream comprises Physical Uplink Shared Channel (PUSCH) transmission or Physical Uplink Control Channel (PUCCH) control information.
 16. The method of claim 11, wherein the method is performed by a wireless transmit/receive unit (WTRU), and wherein determining to use the DM-RS transmission schedule is based on whether the WTRU is connected to a small cell or connected to a macro cell.
 17. The method of claim 11, wherein the plurality of DM-RS transmission schedules comprises a legacy DM-RS transmission schedule.
 18. A wireless transmit receive unit (WTRU) comprising: a processor configured to: determine to use a demodulation reference signal (DM-RS) transmission schedule out of a plurality of DM-RS transmission schedules, wherein the DM-RS transmission schedule is characterized by one or more of a DM-RS transmission being mapped to a single orthogonal frequency-division multiplexing (OFDM) symbol of a subframe of a data stream or a DM-RS transmission being mapped to a first subset of subcarriers of an OFDM symbol of a subframe of a data stream and Physical Uplink Shared Channel (PUSCH) transmission or Physical Uplink Control Channel (PUCCH) control information being mapped to a second set of subcarriers of the OFDM symbol, wherein the first set of subcarriers is different than the second set of subcarriers; and transmit the data stream according to the DM-RS transmission schedule.
 19. The WTRU of claim 18, wherein the processor is configured to determining to use the DM-RS transmission schedule based on whether the WTRU is connected to a small cell or based on whether the WTRU is connected to a macro cell.
 20. The WTRU of claim 18, wherein the plurality of DM-RS transmission schedules comprises a legacy DM-RS transmission schedule. 